Eighteen owl monkeys (Aotus trivirgatus) and four squirrel monkeys (Saimiri sciureus) developed intracerebral gliomas that were predominantly astrocytic in cell type. This is the completion of the studies using 92 owl monkeys and 15 quirrel monkeys that were inoculated in 1978 with JC virus, a human polyomavirus or control material. The monkeys were monitored for 36 months (August, 1981) before the studies were terminated. Additional owl and squirrel monkeys were inoculated with JC virus or control material. Animals developing intracerebral tumors from this group of monkeys will be studied using positron emission tomography or autoradiography. Some of the tumor material from the monkeys will be used to complete hybridization studies between JC virus DNA and DNA extracted from tumor cells to delineate portions of JC virus DNA present in the tumor genome.